In imaging systems such as a thermal printer in which a colorant donor element is placed over a medium for receiving an image, a focus position can vary due to various characteristics of the imaging system. For example, the flatness of the colorant donor material and the roundness of an imaging drum of the thermal printer can effect focus position. This creates the need for changing a focus position without compromising image quality. In the above-mentioned co-pending U.S. patent application Ser. No. 08/865,792, reflecting members or surfaces comprised of prisms are disclosed. In this arrangement, a focus distance from a laser to a donor can be changed without moving either the lens or the donor, by providing for a movement of one prism with respect to three stationary prisms.
FIG. 1 illustrates a focusing apparatus 10 such as shown in co-pending U.S. patent application Ser. N0 08/865,792. As illustrated in FIG. 1, focusing apparatus 10 includes reflecting members in the form of a first prism 11, a second prism 20, a third prism 30 and a fourth prism 40. Prisms 11, 30 and 40 are preferably cemented together utilizing suitable bonding material such as UV curable adhesives.
As further illustrated in FIG. 1, a fiber array 50 is located at a face 12 of prism 11 and light is reflected off of an interface 14 of prism 11 and prism 40. This light then enters prism 20 through its hypotenuse 22 and is reflected off first face 24 and second face 26 of prism 20. Light exits hypotenuse 22, reflects off of interface 32 of prisms 30 and 40 and exits prism 30 as it travels to a lens 60.
As disclosed in co-pending U.S. patent application Ser. No. 08/865,792, a focus shift can be produced by moving prism 20 relative to symmetric group of prisms 11, 30 and 40. When moving prism 20 in vertical direction 5 (Y axis), it is important that no other motion, such as tipping, tilting or movement in a direction parallel to lens 60 and optical axis 6 (x-axis) be incidentally allowed to occur.
U.S. Pat. No. 4,763,967 discloses an arrangement for supporting a lens. However, in this patent, the support makes up part of a resonant system for maintaining the natural frequency of movement of the lens, as opposed to forming a part of an assembly that permits a controlled movement of a reflecting member, such as a prism, along a first axis, or part of an assembly which permits a controlled movement of a prism along a first axis relative to a further prism and/or lens. Additionally, suspension or supporting systems such as disclosed in U.S. Pat. Nos. 4,538,882 and 4,720,088 permit two degrees of freedom. However, when moving a prism such as discussed above, it is important that the prism move in one direction without tipping or tilting.